Molding materials composed of reinforcing fibers and a thermoplastic resin are widely used in sports goods applications, aerospace applications and general industrial applications because they are lightweight and have excellent dynamic characteristics. Reinforcing fibers to be used in these molding materials reinforce molding articles in various ways depending on their use application. For those reinforcing fibers, metal fibers such as aluminum fibers and stainless fibers, organic fibers such as aramid fibers and PBO fibers, inorganic fibers such as silicon carbide fibers, and carbon fibers are used. From the viewpoint of a balance of specific strength, specific rigidity and lightness, carbon fibers are suitable, and among them, polyacrylonitrile-based carbon fibers are suitably used.
Further, as molding materials including a continuous reinforcing fiber bundle and a thermoplastic resin as a matrix, a variety of forms such as thermoplastic prepregs, yarns and glass mats (GMT) are known. Those molding materials facilitate molding by taking advantage of the characteristics of a thermoplastic resin, do not require a load for storage unlike a thermosetting resin, provide molded articles having high toughness, and are excellent in recyclability. Particularly, molding materials processed into a pellet shape are applicable to a molding method excellent in economy and productivity such as injection molding or stamping molding, and are thus useful as industrial materials.
However, in fact, such molding materials are not so widely used because impregnation of a continuous reinforcing fiber bundle with a thermoplastic resin in the process of producing a molding material has problems in economy and productivity. For example, it is well known that a resin having a higher melt viscosity is more difficult to impregnate to a reinforcing fiber bundle. A thermoplastic resin excellent in dynamic characteristics such as toughness and elongation is a particularly high-molecular-weight body, thus has a viscosity higher than that of a thermosetting resin, requires a higher process temperature, and is therefore unsuitable to easily produce a molding material with high productivity.
On the other hand, when a thermoplastic resin having a low molecular weight, i.e. a low viscosity is used as a matrix resin for ease of impregnation, there is the problem that the dynamic characteristics of the resulting molded article are considerably deteriorated.
Japanese Patent Laid-open Publication No. 10-138379 discloses a molding material in which a high-molecular-weight thermoplastic resin is disposed in contact with a composite composed of a low-molecular-weight thermoplastic polymer and a continuous reinforcing fiber bundle.
In that molding material, a low-molecular-weight body is used for impregnation of a continuous reinforcing fiber bundle, while a high-molecular-weight body is used as a matrix resin so that not only economy and productivity but also dynamic characteristics are secured. When the molding material is molded by an injection molding method, reinforcing fibers are easily mixed with a matrix resin while breakage of the reinforcing fibers is minimized in plasticization of the material during molding, and thus a molded article excellent in dispersibility of fibers can be produced. Therefore, the resulting molded article can include reinforcing fibers having a larger fiber length than before, and have both good dynamic characteristics and excellent external appearance quality.
In recent years, however, fiber-reinforced composite materials have increasingly received attention, and come into use in a variety of segmented applications so that a molding material further excellent in moldability, handling characteristics, and dynamic characteristics of the resulting molded article has been required, and it has become necessary to further improve economy and productivity from an industrial point of view. A wide variety of technical developments have become necessary to, for example, reduce a process load by further improving the impregnation property of a low-molecular-weight body, propose a molding material having further improved heat resistance, improve dynamic characteristics by increasing the fiber length by improving fiber dispersibility during molding, and further improve the surface external appearance.
Japanese Patent Laid-open Publication No. 2008-231291 discloses a molding material in which a high-molecular-weight thermoplastic resin is disposed in contact with a composite composed of a polyarylene sulfide prepolymer and continuous reinforcing fibers. The polyarylene sulfide prepolymer is an excellent material easily impregnated to a reinforcing fiber bundle to improve the productivity of a molding material, and is easily dispersible in or compatible with a matrix resin in a molding step to improve dispersion of reinforcing fibers in a molded article. However, the polyarylene sulfide prepolymer has a high melting temperature of about 200 to 260° C., and requires a high temperature of 200° C. or higher for impregnating reinforcing fibers with the polyarylene sulfide prepolymer. When the impregnation temperature becomes high, i.e. 200° C. or higher, fuzz of reinforcing fibers may easily occur in an impregnation step, leading to deterioration of productivity due to thread breakage caused by fuzz, or necessity of removal of fuzz. One method of improving productivity of the molding material may be the use of a substance that takes the place of a polyarylene sulfide prepolymer and has a low melting temperature.
Japanese Patent Laid-open Publication No. 2012-57277 discloses a molding material with a thermoplastic resin bonded to a reinforcing fiber bundle in which an epoxy resin satisfying specific conditions is heated and melted, and impregnated to the reinforcing fiber bundle. The disclosed epoxy resin has a relatively low melting temperature, and is impregnated to reinforcing fibers at about 150° C., and productivity is improved as compared to the technique in Japanese Patent Laid-open Publication No. 2008-231291. However, the dynamic characteristics of a molded article obtained by molding the molding material are not sufficient, and development of a molding material having both productivity and high dynamic characteristics is desired.
Particularly among matrix resins, resins having high heat resistance, for example, carbonates having a glass transition temperature of 140° C. or higher, and thermoplastic resins classified as super engineering plastics and having extremely high heat resistance are used as alternative materials of metals for the purpose of reducing the body weight in automobile fields, and increasingly used in electric and electronic fields because the use of lead-free solder is increased from an environmental point of view, a higher temperature is necessary for melting solder, and resultantly a resin material to be used is increasingly required to have more strict heat resistance.
While heat-resistant resins have come into wide spread use, a high process temperature is necessary as a matter of course for molding these resins, and thus a molding material having good workability and handling characteristics in such a process has become necessary.
Japanese Patent Laid-open Publication No. 2008-231291 discloses a molding material in which a high-molecular-weight thermoplastic resin is disposed in contact with a composite composed of a polyarylene sulfide prepolymer and continuous reinforcing fibers. The polyarylene sulfide prepolymer is an excellent material easily impregnated to a reinforcing fiber bundle to improve the productivity of a molding material, and is easily dispersible in or compatible with a matrix resin in a molding step to improve dispersion of reinforcing fibers in a molded article. However, there are still problems in interface strength between reinforcing fibers and the matrix resin, and further improvement of dynamic characteristics is desired.
Further, a master batch to be used in these molding materials is a molding material in which additives for imparting functions such as strength, impact resistance, flame retardancy and colorization are blended in a resin beforehand, and the functions can be exhibited by blending only a small amount of the master batch in a matrix resin. Many of additives are in the form of a powder or a fine flake, and therefore often difficult to handle. They are more easily handled when formed into a master batch in use, and therefore the master batch is widely used to modify a resin and impart functions.
Recently, among matrix resins, resins having high heat resistance, for example, carbonates having a glass transition temperature of 140° C. or higher, and thermoplastic resins classified as super engineering plastics and having extremely high heat resistance have been used as alternative materials of metals for the purpose of reducing the body weight in automobile fields, and increasingly used in electric and electronic fields because the use of lead-free solder is increased from an environmental point of view, a higher temperature is necessary for melting solder, and resultantly a resin material to be used is increasingly required to have more strict heat resistance.
While heat-resistant resins have come into wide spread use, a high process temperature is necessary as a matter of course for molding these resins, and thus a master batch having good workability and handling characteristics in such a process has become necessary.
For example, fiber-reinforced thermoplastic resins composed of a thermoplastic resin and reinforcing fibers are excellent in balance between lightness and dynamic characteristics, and are therefore widely used in structural members of aircrafts, automobiles and watercrafts, electric and electronic device cases, sports applications, and industrial materials such as building materials, but because further high heat resistance is required, a master batch capable of modifying a matrix resin, imparting functions thereto, and improving adhesion with reinforcing fibers even at a high temperature is desired.
Japanese Patent Laid-open Publication No. 2013-49790 discloses a master pellet formed by adding to polyester an end-capping agent containing a carbodiimide compound, and melting and kneading the mixture by an extruder. Application of that master pellet as a master batch is considerably limited because the matrix resin varies for a resin other than polyester.
On the other hand, Japanese Patent Laid-open Publication No. 5-86291 and Japanese Patent Laid-open Publication No. 10-251918 each disclose a resin composition and fibers in which a master batch with a carbodiimide compound added to polyphenylene sulfide is used. Those methods do not describe the state of existence of the carbodiimide compound in the master batch, and mere addition of the carbodiimide compound causes the problem that when the master batch is stored in a once unsealed bag, the carbodiimide absorbs water to reduce exhibition of intended functions.
In view of the problems of the conventional techniques, it could be helpful to provide a molding material having a good impregnation property to a reinforcing fiber bundle at 200° C. or lower, and that is capable of achieving high productivity and ensures that a molded article having high dynamic characteristics can be produced. Further, it could be helpful to provide a molding material that ensures that a molded article having high dynamic characteristics can be produced and is excellent in blocking resistance and excellent in handling characteristics. Further, it could be helpful to provide a master batch having improved handling characteristics particularly in a high-temperature molding process at 300° C. or higher, and that is excellent in functional stability during storage.